Re: rfc/rft: use r10 as current on x86-64

[Andreas Steinmetz <ast@domdv.de>]

Brian Gerst wrote:
> Andi Kleen wrote:
> 
>> On Tue, Nov 22, 2005 at 11:52:04AM -0500, Benjamin LaHaise wrote:
>>
>>> Hello Andi et al,
>>>
>>> The patch below converts x86-64 to use r10 as the current pointer
>>> instead of gs:pcurrent.  This results in a ~34KB savings in the code
>>> segment of the kernel.  I've tested this with running a few regular
>>> applications, plus a few 32 bit binaries.  If this patch is
>>> interesting, it probably makes sense to merge the thread info
>>> structure into the task_struct so that the assembly bits for syscall
>>> entry can be cleaned up.  Comments?
>>
>>
>> I think you could get most of the benefit by just dropping
>> the volatile and "memory" from read_pda(). With that gcc would
>> usually CSE current into a register and it would would work essentially
>> the same way with only minor more .text overhead, but r10 would be still
>> available.
> 
> 
> It seems that GCC is reluctant to use the extended registers anyways
> because of the rex prefix, so I don't think dedicating r10 to current
> will cause that many problems.

Be aware of assembler that uses r10, e.g.
arch/x86_64/crypto/aes-x86_64-asm.S
-- 
Andreas Steinmetz                       SPAMmers use robotrap@domdv.de